Altair
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 Altair. |
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| Observation data Epoch J2000 |
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|---|---|
| Constellation (pronunciation) |
Aquila |
| Right ascension | 19h 50m 47.0s |
| Declination | +08° 52' 06" |
| Apparent magnitude (V) | 0.77 |
| Characteristics | |
| Spectral type | A7 IV-V |
| U-B color index | 0.08 |
| B-V color index | 0.22 |
| Variable type | DelSct |
| Astrometry | |
| Radial velocity (Rv) | −26.1 km/s |
| Proper motion (μ) | RA: 536.82 mas/yr Dec.: 385.54 mas/yr |
| Parallax (π) | 194.97 ± 0.86 mas |
| Distance | 16.73 ± 0.07 ly (5.13 ± 0.02 pc) |
| Absolute magnitude (MV) | 2.22 |
| Details | |
| Mass | 1.7 M☉ |
| Radius | 1.7 R☉ |
| Luminosity | 10.7 L☉ |
| Temperature | 8,000 K |
| Metallicity | 200% Sun |
| Rotation | 6.5–10.4 hours |
| Age | <109 years |
| Other designations | |
Altair (α Aql / α Aquilae / Alpha Aquilae / Atair) is the brightest star in the constellation Aquila and the twelfth brightest star in the nighttime sky, at visual magnitude 0.77.
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[edit] Description
Altair is a vertex of the Summer Triangle. It is an "A" type or white star located 17 light years away from Earth (about 159 trillion kilometers or 100 trillion miles), one of the closest stars visible to the naked eye. Altair is most notable for its extremely rapid rotation; by measuring the width of its spectral lines, it was determined that its equator does a complete rotation in about 6½ hours (various other sources give 9 hours, or 10.4 hours). For comparison, our Sun requires just over 25 days for a complete rotation. As a result of its rapid rotation, Altair is oblate: its equatorial diameter is at least 22 percent greater than its polar diameter. Recently, images of the surface of Altair have been captured. This is the first visual verification of gravity darkening.
Altair, along with Beta Aquilae and Gamma Aquilae, form the well-known line of stars sometimes referred to as the shaft of Aquila.
[edit] Location
The star's location in the constellation of Aquila is shown in the following map:
[edit] Etymology
The name "Altaïr" is Arabic for "the bird", from the phrase الطير. The spelling "Atair" is also used frequently. The name was given by Arabic astronomers and adopted by Western astronomers.
It is officially known as 河鼓二 (Hégǔ'èr, the Second Star of the Drum at the River, or more literally, Riverdrum II) in Chinese. However, it is more famously known as its other names: 牵牛星 or 牛郎星 (the Star of the Cowherd), after the Cowherd in the Chinese mythology: the Cowherd and the Weaver Girl; the star's Japanese name of Hikoboshi derives from this same myth.
[edit] Altair in mythology and culture
In Chinese mythology, there is a love story of Qi Xi in which Niu Lang (Altair) and his two children (Aquila -β and -γ) are separated forever from their mother Zhi Nü (Vega) who is on the far side of the river, the Milky Way. The Japanese Tanabata festival is also based on this legend.
In astrology, the star Altair was ill-omened, portending danger from reptiles.
The NASA Constellation Program announced "Altair" as the name of the Lunar Surface Access Module (LSAM) on December 13, 2007.
[edit] See also
[edit] External links
- Report on ultra high-resolution photograph.
- SolStation
- Secrets of Sun-like star probed
- Astronomers Capture First Images of the Surface Features of Altair
